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Guide to vacuuming building cavities to screen for particles, dust, or mold:
This article explains the advantages and shortcomings of using vacuum cassettes or spore traps to collect mold test samples (or other dust or particle samples) from building wall and ceiling cavities. In this article series discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.
Validity/Accuracy of Vacuuming Building Cavities for a Hidden Mold Screen
15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005, Updated 4/14/2009
Vacuuming building cavities is a popular screening practice to look for mold
reservoirs. The investigator is trying to explore wall cavities while doing
minimal or no visible damage.
A wall-check™ system has been marketed for this
purpose and several manufacturers have coped the basic idea: a receiving
Air-o-Cel™ or MCE filter cassette is attached at its inlet side to a tube which
is inserted as a probe into a wall cavity, permitting creation of only a small
hole. The outlet or pump side of the test device is connected to a pump and
operated, typically at 15 lpm. Where we have tested this method we have
experimented with both passive collection (what most investigators use) or
aggressive collection (banging on the wall/ceiling at various points to attempt
to dislodge and stir particles).
Short duration samples, 1-2 minutes using an Air-o-Cell ™ permit a
comparatively large number of samples to be collected in a reasonably short
interval. Long duration samples, perhaps for up to two hours, are collected
using an MCE filter cassette.
Wall Cavity Vacuuming - Found Ineffective
Working with Louis Relle, a Louisiana mold remediation expert on a New
Orleans Building which was to be demolished we collected wall-check samples from every suspect Building cavity.
building interior surfaces were demolished we then performed a visual inspection and collected bulk surface samples using tape.
See DUST / MOLD TEST KIT INSTRUCTIONS
The wall check samples were
completely unable to detect large and significant mold contamination in the cavities of this building.
We postulate that
even with mechanical agitation (banging on the wall during wall check sampling) the flow rate of the sampling method does
not move enough air to reliably pick up surface contamination unless the mold genera/species happens to be at a
particularly high state of active sporulation. The tool remains in the professional's arsenal, to be used with
Shortcomings of vacuuming building cavities through a tube but our testing
strongly suggests that this method is very unreliable for characterizing wall
contents. We do not believe that enough air movement is created in the wall
cavity (sucking any lpm flow through a small diameter tube) to reliably collect
what could be a severe mold reservoir that happens not to be right next to the
probe. Further if the cavity is insulated there will be virtually no air or
particle movement except from very close to the probe.
What should we make of wall vacuum test results done without
other inspection and testing?
cavity vacuum tests, depending on how and when they are performed, can be
like searching for a needle in a haystack while looking through a straw: if you
find evidence of a problem you're lucky. But if you don't find evidence, when
using a very limited-scope method, that doesn't mean that a problem is not
Our photo, left, is not showing the wall-check vacuum method that relies on vacuuming into a cassette through a hole in the wall. Instead, here we have pulled loose paneling and have inserted our spore trap cassette into the cavity.
This position combined with aggressive sampling by banging on the wall paneling with a flashlight is more likely to collect problem particles if they are present close to the point of vacuum cassette insertion into the wall. But even this approach is not a reliable characterization of mold risk in the building. And it is not looking into the wall cavity itself - rather we are looking at the two surfaces behind the paneling.
Short vacuum pump duration for microscopic examination (to avoid
sample overload, e.g. 2-=3 minutes on an Air-O-Cell) does not move enough air
to reliably find what may be in the wall
cavity. An experiment done with Louis Relle in New Orleans LA demonstrated that
wall-vac tests found less than 10% of large problem mold cavities that could
be discovered by cutting drywall openings in a building.
Our photo (left) shows a short-duration but larger surface area or wall opening vacuuming system invented and tested by the author - it did not provide useful results.
Longer vacuum pump duration samples for viable sampling (2 hours
into an MCE cassette for culturing) still may not move enough air to sample
through a cavity, particularly if the cavity is insulated. Further, two-hour
samples means that most-likely very few sample points were collected, making
the inspection scope extremely limited and thus overall confidence in the
accuracy of the picture of the building lower.
Consider that the popularly-marketed version of this wall cavity vacuuming approach
to test for hidden mold contamination in buildings relies on culture of the sample. Did you know that only about 10% of molds grow
in any culture at all? You're 90% uncertain of the accuracy of the test at the
One can't be sure that the mold that grew in the culture represents the
dominant problem mold or whether it's just a low-occurrence (in the building) spore
that liked the media (in the culture). We like cultures for further
genera/species identification of samples but we are nervous about relying on them
to tell me if the building has a problem or not.
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